Medical image display apparatus and control method therefor

ABSTRACT

A medical image display apparatus which displays, in a display screen, a display image having undergone gray level transform of changing number of gray levels of a medical image, obtains a representative value of pixel values concerning a region of a block, in the medical image, which corresponds to each partial region in a region designated in the display image. The medical image display apparatus sets a specific region in the display screen so as to include the designated region, and superimposes/displays and arranges obtained representative values on the specific region in correspondence with the arrangement of the partial regions.

TECHNICAL FIELD

The present invention relates to a medical image display apparatus, acontrol method, and a program.

BACKGROUND ART

With recent advances in the digitization of medical data, various typesof medical images are archived as digital images, and doctors haveincreasing chances of performing image diagnosis upon displaying digitalimages on displays. In general, medical images are stored in formatscomplying with DICOM (Digital Imaging and Communications in Medicine)international standards. Medical images include CT (Computed Tomography)images and MRI (Magnetic Resonance Imaging) images. Each type of imageincludes a large amount of three-dimensional image data constituted bymany tomographic images. A medical image display apparatus is used toefficiently and meticulously observe such a large amount of image data.

A conventional medical image display apparatus has, as display functionsfor tomographic images, a function of moving a tomographic position, afunction of enlarging/reducing an overall image, a function oftranslating a display position, a gray level transform function, and thelike. In this case, the gray level transform function is a function oftransforming each pixel value of a gray scale according to apredetermined rule. In general, a CT image is expressed by a 12-bit graylevel (4,096 gray levels) HU (Hounsfield Unit) value per pixel, which isstored as a pixel value. When a doctor observes a CT image, a medicalimage display apparatus displays the CT image upon transforming the HUvalues into the number of gray levels suitable for display. In thistransform, 12-bit gray level pixel values are transformed into 8-bitgray levels by using, for example, two gray level transform parameters,that is, WC (Window Center) and WW (Window Width), defined by DICOMstandards. That is, the image (display image) having simultaneouslyundergone a change in the number of gray levels and a change in graylevel distribution is displayed on a display. This makes it easy to seethe difference in HU value (gray level difference) between a specificorgan and a tissue. For an image other than a CT image (for example, anMRI image, PET image, or ultrasound image), gray level transform similarto that described above is performed to make it easy to see thedifferences between pixel values (gray level differences).

Although the above gray level transform function makes it easy to seeimage gray level differences, this rather makes it difficult to seeoriginal pixel values (HU values of a CT image) (before changes in thenumber of gray levels and gray level distribution). For this reason,some computer software has a function of displaying the original pixelvalue of each pixel in numerical string. For example, as shown in FIG.6, when the user designates a target region by drawing a rectangle(graphic 52), the software obtains an image in the target region,enlarges and displays the image in another window 62 at a highmagnification, and displays the original pixel value (HU value) of eachpixel on the enlarged image.

Computer software used in general has an enlarged display functioncalled loupe function for a frame in a rectangular region, as shown inFIG. 7. With the loupe function, when the user moves the cursor, thesoftware generates a frame by enlarging a frame in a rectangular regionwith a predetermined size centered on the cursor position at apredetermined magnification, and displays the frame (graphic 63). Inthis case, the software displays the enlarged frame such that its centercoincides with the cursor position(http://www.mathworks.co.jp/jp/help/images/ref/impixelregion.html).

When using a medical image display apparatus like that described above,there are demands to see a display image before enlargement, that is, anoverall image, and simultaneously see an enlarged image in a targetregion and each pixel value in the target region. However, in the abovepixel value display, since a display image and each pixel value arerespectively displayed in windows at different positions, it isdifficult for the user to simultaneously see them. On the other hand,when using the loupe function, although an enlarged frame is displayedat the cursor position, the frame before enlargement is hidden in theregion where the enlarged frame is displayed. Even if, therefore, thepixel value display function is combined with the loupe function, theabove problem cannot be solved.

SUMMARY OF INVENTION

An embodiment of the present invention is made in consideration of theabove problem and provides a display function which makes it possible tosimultaneously see a display image and each pixel value in a targetregion.

According to one aspect of the present invention, there is provided amedical image display apparatus which displays, in a display screen, adisplay image having undergone gray level transform that is changingnumber of gray levels of a medical image, the apparatus comprising:obtaining means for obtaining a representative value of pixel valuesconcerning a region of a block, in the medical image, which correspondsto each partial region in a region designated in the display image;setting means for setting a specific region in the display screen so asto include the designated region; and display control means forsuperimposing/displaying and arranging representative values obtained bythe obtaining means on the specific region in correspondence with anarrangement of the partial regions.

According to another aspect of the present invention, there is provideda method of controlling a medical image display apparatus whichdisplays, in a display screen, a display image having undergone graylevel transform of changing number of gray levels of a medical image,the method comprising: an obtaining step of obtaining a representativevalue of pixel values concerning a region of a block, in the medicalimage, which corresponds to each partial region in a region designatedin the display image; a setting step of setting a specific region in thedisplay screen so as to include the designated region; and a displaycontrol step of superimposing/displaying and arranging representativevalues obtained in the obtaining step on the specific region incorrespondence with an arrangement of the partial regions.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of the overall arrangementof a medical image display system according to an embodiment;

FIG. 2 is a flowchart showing an example of image display processing bythe medical image display apparatus;

FIG. 3 is a flowchart showing an example of enlarged display processingby the medical image display apparatus;

FIG. 4 is a view showing an example of a frame displayed on a displayunit;

FIG. 5 is a view showing an example of a frame displayed on the displayunit;

FIG. 6 is a view showing a frame display example using a pixel valuedisplay function; and

FIG. 7 is a view showing a frame display example using a loupe function.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the present invention will be described indetail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of the overall arrangementof a medical image display system including a medical image displayapparatus according to an embodiment. The medical image display systemincludes a medical image display apparatus 10 and a database 22. Theseapparatuses are communicatively connected to each other via acommunication means. In this embodiment, a LAN 21 (Local Area Network)is used as such a communication means. The database 22 manages andstores medical information such as medical images. The medical imagedisplay apparatus 10 obtains medical images managed by the database 22via the LAN 21.

The composition of the medical image display apparatus 10 will bedescribed as follows. The medical image display apparatus 10 includes acommunication IF 31, a ROM 32, a RAM 33, a storage unit 34, an operationunit 35, a display unit 36, and a control unit 37. The communication IF(Interface) 31 is implemented by, for example, a LAN card or the like,and controls communication between an external apparatus (for example,the database 22) and the medical image display apparatus 10 via the LAN21. The ROM (Read Only Memory) 32 is implemented by a nonvolatile memoryor the like, and stores various types of programs and the like. The RAM(Random Access Memory) 33 is implemented by a volatile memory or thelike, and temporarily stores various types of information. The storageunit 34 is implemented by, for example, an HDD (Hard Disk Drive) or thelike, and stores various types of information. The operation unit 35 isimplemented by, for example, a keyboard, a mouse, and the like, andinputs instructions from the user into the apparatus. The display unit36 is implemented by, for example, a display or the like, and displaysvarious types of information to the user (for example, a doctor).

The control unit 37 is implemented by, for example, a CPU (CentralProcessing Unit) or the like, and comprehensively controls processing inthe medical image display apparatus 10. The control unit 37 is providedwith, as its functional components, an image readout unit 41, a targetregion obtaining unit 42, a target image obtaining unit 43, a gray leveltransform unit 44, an image generation unit 45, a display control unit46, a statistics calculation unit 47, and a character string generationunit 48. These components can be implemented by making a CPU (not shown)read out programs stored in the ROM 32, the storage unit 34 or the likeusing the RAM 33 as a work area and execute the programs. Note that someor all of these components may be implemented by dedicated circuit(s)and the like.

The image readout unit 41 reads out a medical image (first image) fromthe database 22 via the communication IF 31 and the LAN 21. For the sakeof easy understanding, the following description will exemplify amedical image complying with DICOM standards. However, the presentinvention can be easily applied to other types of images. In addition,the following will exemplify a case in which one medical image isdisplayed. Obviously, however, the present invention can be easilyapplied to a case in which a three-dimensional medical image constitutedby many tomographic images like a CT image or MRI image is displayed.When, for example, applying the present invention to a three-dimensionalmedical image, an arbitrary tomographic image in a three-dimensionalmedical image is displayed in a predetermined region on the screen ofthe display unit 36. Processing in this embodiment may then be appliedto the displayed tomographic image. Note that the tomographic image tobe displayed on the screen of the display unit 36 can be arbitrarilychanged in accordance with an instruction from the user.

The gray level transform unit 44 performs gray level transform(including a change in the number of gray levels and a change in graylevel distribution) of images (first and second images) based on the WCand WW values defined in DICOM standards. Note that the second imagewill be described later. Since WC and WW values are written in theheader portion of a DICOM image, the gray level transform unit 44 canperform gray level transform by using the WC and WW values written inthe header portion. Note that a GUI (Graphical User Interface) forchanging WC and WW values may be displayed on the display unit 36 tomake it possible to change the WC and WW values in accordance with auser input inputted from the operation unit 35. The gray level transformunit 44 can perform gray level transform desired by the user byperforming gray level transform using the WC and WW values changed viathe GUI. In general, a CT image is expressed by a 12-bit gray level(4,096 gray levels) HU (Hounsfield Unit) value per pixel, which isstored as a pixel value. The gray level transform unit 44 performs graylevel transform by using WC and WW values to convert each 12-bit graylevel pixel value into an 8-bit gray level (256 gray levels), therebyobtaining a display image to be displayed on the display unit 36. Notethat when the display unit 36 is configured to directly display an imagebefore gray level transform, the gray level transform unit 44 may beomitted.

The display control unit 46 displays the first image (display image)after gray level transform by the gray level transform unit 44 in apredetermined region (a window in the GUI) on the screen of the displayunit 36. In addition, the display control unit 46 displays a graphicindicating the target region obtained by the target region obtainingunit 42 (to be described later) on the screen of the display unit 36.Furthermore, the display control unit 46 has a function ofsuperimposing/displaying a second image (to be described later) on adisplay image and a function of superimposing/displaying arbitrarycharacter strings on an arbitrary image. The display control unit 46 canalso translate the display position (X- and Y-coordinates) of a displayimage and change a display size (enlargement ratio) in accordance withinstructions from the user. In synchronism with such translation of thedisplay position and change in display size, the display control unit 46translates information (graphic or character strings) superimposed on adisplayed image or change the display size. Even when information istranslated or a display size is changed, the relative positionalrelationship between the display image and the image (information)superimposed/displayed on it is maintained.

The target region obtaining unit 42 obtains information indicating anarbitrary position (the position designated by the user) on the firstimage (that is, the display image) after gray level transform displayedon the display unit 36 in accordance with a user input inputted from theoperation unit 35. In the medical image display apparatus according tothis embodiment, user input can be implemented by, for example,operating the pointing device (for example, the mouse) of the operationunit 35. Position information on an image which is designated by thepointing device is calculated from an image display position on thescreen of the display unit 36 and a cursor position corresponding to theoperation of the pointing device. The target region obtaining unit 42obtains, as a target region, a rectangular region with a predeterminedsize centered on the position designated by the pointing device.

The target image obtaining unit 43 obtains, as a target image, an imagecorresponding to the target region, in the first image read out by theimage readout unit 41, which is designated by the target regionobtaining unit 42. Assume that the target region can be divided intoblocks (partial regions) each having a predetermined size. Thisembodiment will exemplify a case in which each partial region in atarget region is formed from one pixel. In this case, the representativevalue of each block (each pixel) of the target image obtained from thefirst image is exactly the pixel value of one pixel in the block. Notethat a partial region (block) is constituted by a predetermined numberof adjacent pixels, for example, a total of four pixels of 2 pixels(vertical)×2 pixels (horizontal), it is possible to use the value (forexample, the statistic) calculated from the four pixels constituting theblock as the representative value of a block of the target image. Forexample, the value to be calculated as a representative value includesthe average value or median value of four pixel values. It is alsopossible to allow the user to set the size of such a partial region as“m×n pixels” (where m and n are natural numbers) using, for example, theoperation unit 35.

The image generation unit 45 generates an enlarged image by enlarging atarget image at predetermined magnifications (enlargement ratios) in thevertical and horizontal directions. In this case, the enlargement ratiosin the horizontal and vertical directions may be the same or differentvalues. Alternatively, the user may be allowed to change the respectiveenlargement ratios in the vertical and horizontal directions via a GUI.Furthermore, the image generation unit 45 replaces the color of part ofthe enlarged image (a portion determined in accordance with apredetermined rule) with a transparent color (a background transparentportion). A description will be made later about which portion of theenlarged image is to have a transparent color. With the aboveprocessing, the image generation unit 45 generates the second image.That is, the second image is the image obtained by replacing the colorof part of the enlarged image generated by enlarging the target imagewith a transparent color. When the second image issuperimposed/displayed on the first image, the first image can be seenthrough the transparent portion of the first image. Alternatively, theimage generation unit 45 may generate the second image by making theoverall enlarged image translucent by setting a predeterminedtransmittance for the overall enlarged image. Note that a technique ofmaking a portion or all of an image transparent or translucent isgenerally known as an image display technique using an α plane(information for designating a transmittance for the image for eachpixel position).

The statistics calculation unit 47 calculate the statistics (forexample, the average, variance, maximum value, and minimum value) of thepixel values of all the pixels of the target image obtained by thetarget image obtaining unit 43. The character string generation unit 48obtains the representative value (a pixel value in this embodiment) ofeach block of the target image obtained by the target image obtainingunit 43 and the statistics calculated by the statistics calculation unit47 (numerical values obtaining function). The character stringgeneration unit 48 generates character strings expressing thesenumerical value data in numerals (character string generation function).The character string generation unit 48 also decides a display form (forexample, a display color, line width, and ornamental writing) for eachcharacter string corresponding to each pixel value based on each pixelvalue of the target image (in accordance with a predetermined rule)(display form changing function). Note that a specific example of amethod of deciding a display form will be described later.

Next, an example of a processing procedure in the medical image displayapparatus 10 shown in FIG. 1 will be described as follows with referenceto FIGS. 2 to 5.

FIG. 2 is a flowchart showing an example of a procedure for imagedisplay processing in the medical image display apparatus 10. FIGS. 4and 5 are respectively the first and second examples of screensdisplayed on the display unit 36. Referring to FIGS. 4 and 5, asindicated by them, the X-axis is taken in the right direction, and theY-axis in the down direction.

When the user issues an instruction to read out the first image via theoperation unit 35, the processing shown in FIG. 2 starts. In step S101,the image readout unit 41 of the medical image display apparatus 10reads out the first image (medical image) from the database 22 via thecommunication IF 31 and the LAN 21, and stores the image in the RAM 33.In step S102, the gray level transform unit 44 reads out the first imagefrom the RAM 33, and generates a display image (the first image aftergray level transform) by performing gray level transform with respect tothe first image. The display control unit 46 then displays the displayimage in a predetermined display region (a window 51 in FIG. 4) on thescreen of the display unit 36 (step S102). In step S103, the controlunit 37 substitutes 0 (a value indicating that enlarged display is notbeing performed) into an enlarged display in-process flag, and stores itin the RAM 33.

When a user input is obtained from the operation unit 35 in step S104,the control unit 37 determines in step S105 whether the obtained userinput is a processing end command. If the user input is a processing endcommand (YES in step S105), the processing in FIG. 2 is terminated. Ifthe user input is not a processing end command (NO in step S105), theprocess advances to step S106, in which the control unit 37 determineswhether the user input is an enlarged display start command. If the userinput is an enlarged display start command (YES in step S106), theprocess advances to step S110. If the user input is not an enlargeddisplay start command (NO in step S106), the process advances to stepS107.

In step S107, the control unit 37 determines whether the user input isan enlarged display end command. If the user input is an enlargeddisplay end command (YES in step S107), the process returns to stepS103. If the user input is not an enlarged display end command (NO instep S107), the process advances to step S108. In step S108, the controlunit 37 reads out the enlarged display in-process flag from the RAM 33to determine whether the flag is 1 or 0, that is, whether the enlargeddisplay is in process. If the user input is an enlarged displayin-process flag (YES in step S108), the process advances to step S109.If the user input is not an enlarged display in-process flag (NO in stepS108), the process returns to step S104. In step S109, the control unit37 determines whether the user input is a cursor movement command. Ifthe user input is a cursor movement command (YES in step S109), theprocess advances to step S111. If the user input is not a cursormovement command (NO in step S109), the process returns to step S104.

In step S110, the control unit 37 substitutes 1 (a value indicating thatenlarged display is being performed) into the enlarged displayin-process flag, and stores it in the RAM 33. In step S111, the medicalimage display apparatus 10 performs enlarged display processing. Theenlarged display processing in step S111 will be described in detailwith reference to FIG. 3.

FIG. 3 is a flowchart showing an example of a procedure for enlargeddisplay processing (step S111 in FIG. 2) in the medical image displayapparatus 10. In step S201, the target region obtaining unit 42 obtainsa target region on the first image in the following procedure. First ofall, the target region obtaining unit 42 obtains a cursor positionP₀(x₀, y₀) on the screen of the display unit 36 and a display regionR₁{(x_(s1), y_(s1)), (x_(e1), y_(e1))} (the window 51 in FIG. 4). Inthis case, x₀ and y₀ respectively represent the X- and Y-coordinates ofthe cursor position P₀, and (x_(s1), y_(s1)) and (x_(e1), y_(e1))respectively represent the X- and Y-coordinates of an upper leftposition and lower right position in the display region R₁ of the imagein the order named.

The target region obtaining unit 42 then obtains a target regionR₂{(x_(s2), y_(s2)), (x_(e2), y_(e2))} (a graphic 52 in FIG. 4) having atarget region size (w, h) centered on the cursor position P₀(x₀, y₀)according to equations (1) to (4) given below. In this case, (x_(s2),y_(s2)) and (x_(e2), y_(e2)) respectively represent the X- andY-coordinates of an upper left position and lower right position in thedisplay region R₂ in the order named. Note that in the case shown inFIG. 4, the target region has a target region size (8, 8) of 8 pixels ineach of the vertical and horizontal directions.

x _(s2) =x ₀ −w/2   (1)

Y _(s2) =y ₀ −h/2   (2)

x _(e2) =x ₀ +w/2   (3)

y _(e2) =y ₀ +h/2   (4)

In step S202, the target region obtaining unit 42 determines whether thetarget region R₂{(x_(s2), y_(s2)), (x_(es), y_(e2))} exists in thedisplay region R₁{(x_(s1), y_(s1)), (x_(e1), y_(e1))} of the first image(display image) (step S202). If the target region R₂ exists in thedisplay region R₁ (YES in step 202), the process advances to step S203.Otherwise (NO in step S202), the processing in FIG. 3 is terminated.Note that it is possible to determine whether the target region R₂exists in the display region R₁ according to, for example, equations (5)to (8) given below. That is, if all equations (5) to (8) are met, thetarget region R₂{(x_(s2), y_(s2)), (x_(es), y_(e2))} exists in thedisplay region R₁{(x_(s1), y_(s1)), (x_(e1), y_(e1))} of the firstimage.

x_(s1)≤x_(s2)   (5)

y_(s1)≤y_(s2)   (6)

x_(e1)≥x_(e2)   (7)

y_(e1)≥y_(e2)   (8)

In step S203, the display control unit 46 displays a graphic (thegraphic 52 in FIG. 4) indicating the target region R₂{(x_(s2), y_(s2)),(x_(es), y_(e2))} on the first image. In step S204, the target imageobtaining unit 43 reads out a portion (target image), of the first imagebefore gray level transform, which corresponds to the target regionR₂{(x_(s2), y_(s2)), (x_(es), y_(e2))} from the RAM 33. In step S205,the gray level transform unit 44 executes gray level transform withrespect to the target image read out in step S204. Note that if apartial region of the target region is constituted by a plurality ofpixels (for example, 2×2 pixels), the target image is also constitutedby the representative values of the respective blocks, and the graylevel transform unit 44 executes gray level transform concerning therepresentative values.

In step S206, the image generation unit 45 generates an enlarged imageby enlarging the target image after the gray level transform by the graylevel transform unit 44 at predetermined enlargement ratios in thevertical and horizontal directions. In the case shown in FIG. 4, thesame enlargement ratio (a magnification of m) is set in the vertical andhorizontal direction. The image generation unit 45 further sets atransparent color for part of the enlarged image so as to make itpossible to see through the background (step S206). In this embodiment,the image generation unit 45 sets a transparent color for a lower halfregion (m pixels (horizontal)×m/2 pixels (vertical)) of an enlargedblock (a region of m pixels (horizontal)×m pixels (vertical) as apartial region of the enlarged image which corresponds to one block (onepixel in this embodiment) of the target image. Setting the lower halfregion of each enlarged block to a transparent region in this mannerwill generate an enlarged image (second image) including slit-likebackground transparent portions in the horizontal direction, which isdisplayed as an image 53 (FIG. 4).

According to the above description, the lower half region of an enlargedblock is set to a transparent region so as to form a slit grating in thehorizontal direction as a whole. However, the upper half region may beset to a transparent region instead of the lower half region. Anotherexample is that the second image including slit-like backgroundtransparent portions in the vertical direction is generated by settingthe right half region or left half region (m/2 pixels (horizontal)×mpixels (vertical)) of each enlarged block (m pixels (horizontal)×mpixels (vertical)) to a transparent region upon setting a transparentcolor for it. That is, an enlarged image (second image) having a slitgrating formed in the vertical direction as a whole is generated.

Still another example is that a second image including backgroundtransparent portions in a checkered pattern is generated by alternatelysetting a transparent color for upper and lower half portions (or rightand left half portions) in accordance with pixel positions. In the aboveexample, a transparent color is set for the upper, lower, right, or lefthalf region of each enlarged block. However, the present invention isnot limited to this. A transparent color may be set for a region largeror smaller than a half region. Furthermore, a transparent color settingis not limited to a transparent state and may be made to have apredetermined transparency degree. Alternatively, the image generationunit 45 may set a predetermined transmittance (for example, atransmittance of 50%) for the overall second image to make the overallsecond image translucent.

In step S207, the statistics calculation unit 47 calculates thestatistics of the pixel values of the target image obtained by thetarget image obtaining unit 43 in step S204. In this embodiment, thetarget image obtaining unit 43 calculates, as the statistics, forexample, the average, variance, maximum value, and minimum value of thepixel values in the target image. In step S208, the character stringgeneration unit 48 then generates character strings expressing therespective representative values (pixel values in this case) of thetarget image (step S204) obtained by the target image obtaining unit 43and the statistics (step S207) calculated by the statistics calculationunit 47 in numerals. For example, in the case of a CT image,representative values (pixel values) are HU values. In the case shown inFIG. 4, the respective pixel values of the target image is displayed asa character string 54, and the statistics of the pixel values of thetarget image is displayed as a character string 55. Note that thecharacter string 55 representing the statistics calculated in step S207may be displayed outside the image 53. This is because the statisticscalculated in step S207 are numerical values concerning the overalltarget region, but are not numerical values corresponding to eachpartial region (a one-pixel region in this embodiment).

In addition, the character string generation unit 48 decides the displayattributes (for example, a display form including a display color) ofeach character string corresponding to each pixel value based on eachpixel value (the display color of a non-transparent region in eachenlarged block of the second image) of the enlarged image after graylevel transform (step S208). In the case shown in FIG. 4, the charactercolor is set to white when the display density of the enlarged imageafter gray level transform is less than a predetermined threshold (whenthe display color is near black), while the character color is set toblack when the display density is equal to or more than the threshold(when the display color is near white). A method of deciding a displayform for characters may include, for example, changing the charactercolor to a color other than white and black, changing the font type ofcharacters, and changing the typeface to boldface or lightface or toitalic or non-italic. In addition, it is possible to display a frameborder surrounding a character and decide the display form (color, linetype, and the like) of this frame border. Although the above descriptionhas exemplified the arrangement in which the character string generationunit 48 decides the display form of a character. However, the presentinvention is not limited to this. For example, the same display form maybe set in advance for all characters in the character string generationunit 48, and the display control unit 46 may change the display form ofa character by the same method as described above.

In step S209, the display control unit 46 then superimposes/displays thesecond image and the character stings on the display unit 36. In thiscase, the display control unit 46 displays the second image (the image53 in FIG. 4) at a position (nearly the center of the target region)where the center of the second image almost coincides with the center ofthe graphic (the graphic 52 in FIG. 4) indicating the target region. If,however, as in the case exemplified by FIG. 4, when the transparentregion of the second image is located at a position slightly shiftedfrom the center of the second image, the display position is slightlyshifted so as to locate a graphic indicating a target region in thetransparent region of the second image. For example, in the case shownin FIG. 4, the second image is displayed at a position shifted upward byfour pixels so as to locate the graphic 52 indicating the target region(8×8 pixel region) in the transparent region of the second image.Furthermore, the display control unit 46 superimposes/displays thecharacter strings generated in step S208 on the non-transparent portionof the partial region of the second image. That is, the characterstrings are displayed to coincide with the opaque portion(non-transparent region) of the enlarged block (the m×m pixel region inthe above case) corresponding to the partial region of the target regionof the second image. In this case, if the character strings are longerthan the opaque portion of the enlarged block of the second image, thefont size of the character strings is reduced to make the characterstrings fall within the opaque portion of the enlarged block of thesecond image.

FIG. 5 shows the second example of the screen displayed on the displayunit 36. In the case shown in FIG. 5, the second image (the image 53 inFIG. 5) is displayed at a position where the center of the second imageis shifted from nearly the center of the graphic (the graphic 52 in FIG.5) indicating the target region. If, for example, the graphic 52indicating the target region is located near the boundary of a displayregion (not show) of the image determined by the display control unit46, the display control unit 46 adjusts the display position of theimage 53. For example, when the image 53 is displayed at a positionwhere its center coincides with nearly the center of the graphic 52,part of the image 53 sometimes protrudes from the display region (thewindow 51) of the image. In such a case, the display control unit 46performs the processing of shifting the display position to make theimage 53 fall within the display region. Note that this processing is anoption so that even if part of the image 53 protrudes from the window51, the graphic 52 indicating the target region may be displayed atnearly the center of the image 53.

The above processing provides the effect of allowing the user tosimultaneously see the first image (display image) after gray leveltransform, the graphic indicating the target region, the second image(enlarged image), and the character strings representing the respectivepixel values of the first image before the gray level transform.

(First Modification)

Note that in the above embodiment, the character string generation unit48 decides the display attributes of each character string correspondingto each pixel value based on each pixel value of the enlarged imageafter gray level transform (the display color of the non-transparentregion of the second image) (step S208). However, the present inventionis not limited to this. The display attributes (for example, the displaycolor) of each character string corresponding to each pixel value may bedecided based on each pixel value (or each representative value) of thetarget image obtained from the first image. For example, pixel values(representative values) are classified into a plurality of groupsaccording to predetermined pixel value (representative value) ranges,and the correspondence relationship between each group and a characterdisplay form is determined in advance. It is then possible to determineto which group each pixel value (representative value) of the targetimage obtained from the first image belongs and to decide the displayform of each character string from the correspondence relationshipbetween the group and the display form.

It is preferable to determine in advance pixel value ranges for groupingin consideration of medical or clinical meanings. For example, it isclinically known that the pixel values of a CT image indicate HU values,and HU value ranges are approximately determined for the respectivecomponents in the body as described below. It is therefore preferable todetermine the display colors of characters for the respective HU valueranges. Note that pixel value ranges may be set for HU value rangeswhich are not described below so as to make each HU value range fallwithin either range described below, thereby deciding the correspondencerelationship between all the pixel values and the display forms (displaycolors) of characters. This allows the user to easily understand, fromthe display color of a character string indicating each pixel value(representative value) displayed on the second image, what componentsincluded in the target region.

HU Value as a reference Components in Body (Approximate values) MetalSeveral Thousands Bone Several Hundreds to 1000 Soft Tissue 17 to 80Water  0 to 16 Fat  −1 to −128 Air −1000

According to the above description, the character string generation unit48 is configured to change a display form. However, the character stringgeneration unit 48 may set the same display form for all characters, andthe display control unit 46 may change the display form of a characterby the same method as described above.

(Second Modification)

In addition, it is possible to switch between the method of displayingthe second image and the method of displaying character strings to besuperimposed/displayed to show representative values in accordance witha user instruction. For example, in user input obtaining processing(step S104) shown in FIG. 2, a user instruction for switching betweenthe method of displaying the second image and the method of displayingcharacter strings to be superimposed is obtained (display changinginstruction). In enlarged display processing (step S111), the processingperformed by the image generation unit 45 and/or the display controlunit 46 is partially changed as follows in accordance with a displaychanging instruction. The following exemplifies three types of displaychanging instructions.

The first display changing instruction is used to instruct whether toset a transparent color to part of an enlarged image in the generationof the second image by the image generation unit 45 (step S206). Thesecond display changing instruction is used to instruct whether tosuperimpose/display the second image and character strings on the firstimage or display a display window different from the first image insuperimposed display of the second image and the character strings bythe display control unit 46 (step S209). The third display changinginstruction is used to instruct to inhibit from displaying the secondimage or character strings in superimposed display of the second imageand character strings by the display control unit 46 (step S209).

Assume that an instruction is issued to inhibit from setting atransparent color to part of an enlarged image in accordance with thefirst display changing instruction and display the second image andcharacter strings in a display window different from the first image(display image) after gray level transform in accordance with the seconddisplay changing instruction. In this case, the display screenexemplified in FIG. 6 is obtained. That is, the second image (withoutany transparent region) is displayed in the window 62 different from thewindow 51, together with character strings indicating the representativevalues of the respective partial regions. In this case, since there isno transparent region, the character strings may be located at anypositions in the enlarged blocks. In the case in FIG. 6, a characterstring is arranged in the center of each enlarged block. Note that FIG.6 shows the respective character strings as black characters on thewhite background. However, the present invention is not limited to this.For example, as exemplified by FIGS. 4 and 5, if a display density isless than a predetermined threshold (if a display color is near black),characters may be displayed in a white character color, whereas if adisplay density is equal to or more than the threshold (if a displaycolor is near white), characters may be displayed in a black charactercolor.

Assume that an instruction is issued to inhibit from setting atransparent color to part of an enlarged image in accordance with thefirst display changing instruction and inhibit fromsuperimposing/displaying character strings in accordance with the thirddisplay changing instruction. In this case, the display screenexemplified by FIG. 7 is obtained. That is, although the second image isdisplayed in an enlarged frame 63, no transparent region exists, and nocharacter strings indicating representative values are displayed.

In addition, if an instruction is issued to inhibit from displaying thesecond image in accordance with the third display changing instruction,only character strings indicating representative values are displayed ina specific region (the region in which the image 53 is displayed in FIG.4) in a display image. In this case, since the representative values arearranged at display positions like those shown in FIG. 4, therepresentative values arranged in correspondence with the respectivepositions of the partial regions are superimposed/displayed in aspecific region corresponding to the display region of the second image.

It is possible to implement both the display method characteristic tothe present invention and the method as in the related art by switchingthe display methods in accordance with display changing instructions asdescribed above.

The above embodiment is a typical embodiment of the present invention.However, the present invention is not limited to the embodimentdescribed above with reference to the accompanying drawings and can bemodified as needed within the range in which the spirit of the presentinvention is not changed.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™,a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-246672, filed Nov. 28, 2013 which is hereby incorporated byreference herein in its entirety.

1. A medical image display apparatus which displays, in a displayscreen, a display image having undergone gray level transform that ischanging number of gray levels of a medical image, the apparatuscomprising: an obtaining unit configured to obtain a representativevalue of pixel values concerning a region of a block, in the medicalimage, which corresponds to each partial region in a region designatedin the display image; a setting unit configured to set a specific regionin the display screen so as to include the designated region; and adisplay control unit configured to superimpose/display and arrangerepresentative values obtained by the obtaining unit on the specificregion in correspondence with an arrangement of the partial regions. 2.The apparatus according to claim 1, wherein the display control unitdisplays the representative value in a display form corresponding to therepresentative value when superimposing/displaying the representativevalue.
 3. The apparatus according to claim 2, wherein the displaycontrol unit changes the display form of the representative value inaccordance with a value obtained by processing the representative valueby the gray level transform.
 4. The apparatus according to claim 2,wherein the display control unit classifies representative values into aplurality of groups and changes a display form of a representative valuein accordance with a group to which the representative value belongs. 5.The apparatus according to claim 4, wherein the plurality of groupscomprise ranges of values classified in correspondence with componentsin a body.
 6. The apparatus according to claim 2, wherein a display formof the representative value is changed by changing a display form of acharacter string indicating the representative value.
 7. The apparatusaccording to claim 2, wherein a display form of the representative valueis changed by changing a display form of a frame border surrounding thecharacter string indicating the representative value.
 8. The apparatusaccording to claim 1, further comprising a generation unit configured togenerate an enlarged image of the designated region, wherein the displaycontrol unit superimposes/displays the enlarged image on the specificregion at a predetermined transmittance.
 9. The apparatus according toclaim 1, further comprising a generation unit configured to generate anenlarged image of a region, of the medical image, which corresponds tothe designated region, wherein the generation unit forms a portion ofeach of enlarged blocks corresponding to the blocks of the medical imagein the enlarged image into a transparent portion, and the displaycontrol unit superimposes/displays the enlarged image on the specificregion and superimposes/displays the representative value on anon-transparent region of each of the enlarged blocks.
 10. The apparatusaccording to claim 9, wherein the generation unit generates the enlargedimage with a slit grating being formed in a lateral direction by formingone of lower and upper regions of the enlarged block into a transparentregion.
 11. The apparatus according to claim 9, wherein the generationunit generates the enlarged image with a slit grating being formed in avertical direction by forming one of right and left regions of theenlarged block into a transparent region.
 12. The apparatus according toclaim 9, wherein the setting unit sets a position of the specific regionso as to locate the designated region in a transparent region formed inthe enlarged image.
 13. The apparatus according to claim 1, wherein thepartial region and the block each comprise a one-pixel region, and theobtaining unit obtains a pixel value of a pixel of the block in themedical image as the representative value.
 14. The apparatus accordingto claim 1, wherein the partial region and the block each comprise aregion comprising a plurality of pixels, and the obtaining unit obtainsstatistic(s) of a plurality of pixel values of the block of the medicalimage as the representative value(s).
 15. A method of controlling amedical image display apparatus which displays, in a display screen, adisplay image having undergone gray level transform of changing numberof gray levels of a medical image, the method comprising: an obtainingstep of obtaining a representative value of pixel values concerning aregion of a block, in the medical image, which corresponds to eachpartial region in a region designated in the display image; a settingstep of setting a specific region in the display screen so as to includethe designated region; and a display control step ofsuperimposing/displaying and arranging representative values obtained inthe obtaining step on the specific region in correspondence with anarrangement of the partial regions.
 16. A non-transitory computerreadable storage medium storing a program for causing a computer toexecute a method of controlling a medical image display apparatus whichdisplays, in a display screen, a display image having undergone graylevel transform of changing number of gray levels of a medical image,the method comprising: an obtaining step of obtaining a representativevalue of pixel values concerning a region of a block, in the medicalimage, which corresponds to each partial region in a region designatedin the display image; a setting step of setting a specific region in thedisplay screen so as to include the designated region; and a displaycontrol step of superimposing/displaying and arranging representativevalues obtained in the obtaining step on the specific region incorrespondence with an arrangement of the partial regions.